This invention relates to polyester polymers. More specifically, this invention relates to polyester polymers having temporarily crosslinked polyester molecules.
Polyesters are widely used to manufacture textile fibers and can be manufactured by combining a glycol, such as ethylene glycol, and a carbonyl compound, such as dimethyl terephthalate (DMT) or terephthalic acid (TPA). In the DMT process, DMT reacts with a glycol, such as ethylene glycol, to form a bis-glycolate ester of terephthalate (xe2x80x9cmonomerxe2x80x9d) and a byproduct methanol in an ester exchanger column. The monomer is then polymerized by condensation reactions in one or two prepolymerizers and then a final polymerizer or finisher.
In the TPA process, TPA is combined with a glycol, such as ethylene glycol, to form a slurry at 60xc2x0 C. to 100xc2x0 C. followed by injecting the slurry into an esterifier. A linear oligomer with a degree of polymerization less than 10 is formed in one or two esterifiers (first and second in series, if two) at temperatures from 240xc2x0 C. to 290xc2x0 C. The oligomer is then polymerized in one or two prepolymerizers and then in a final polymerizer or finisher at temperatures from 250xc2x0 C. to 300xc2x0 C. Water is a byproduct of the TPA esterification and polycondensation process.
A problem associated with polyester fibers is their tendency to pill. Pilling is a defect in fabric caused when fibers are rubbed or pulled out of yarns and entangled with intact fibers, forming soft, fuzzy balls on the fabric surface. One of the most common commercial practices to produce pilling resistant fibers is to make lower molecular weight polyester fibers with an intrinsic viscosity of 0.30 to 0.55, which have lower strength and are pill resistant. Unfortunately, spinning is more difficult with lower molecular weight and lower strength polyester fibers.
A temporary crosslinker, brancher, or melt viscosity booster can be used to increase melt viscosity and polymer strength temporarily for better spinning performance. Tetraethoxysilane (TEOS) has been used commercially for many years as a temporary brancher for pilling resistant polyesters made from DMT process. TEOS temporarily crosslinks or branches polyester molecules and increases melt viscosity and strength for spinning. After spinning, the crosslinks break down by hydrolysis in drawing and other processes, thereby obtaining lower molecular weight fibers and offering pilling resistant properties.
Unfortunately, the use of TEOS as a temporary brancher for pilling resistant polyesters is not compatible with the TPA process. A major problem with TEOS is that TEOS forms sands and solids when it reacts with water. Although TEOS is suitable for the DMT process, where there is no water byproduct, the TPA process produces a water byproduct. Therefore, TEOS is not suitable for the TPA process due to the formation of sands and solids by the reaction of TEOS with the water byproduct.
There have been many studies to use permanent crosslinkers such as trimethylolpropane (TMP) and trimellitic acid or its ester to produce pilling resistant fibers. Unfortunately, the permanent crosslinks do not break down after spinning and their pilling resistant properties are only from the increased brittleness from crosslinking. Polymer molecular weight must be high enough for good spinning, but the high molecular weight polymers have poor pilling resistance. Therefore, permanent crosslinkers are fundamentally inferior compared with temporary crosslinkers or branchers such as TEOS.
The TPA process has gradually become a preferred process for manufacturing of polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate, where water is a byproduct. Therefore, there is an increased need to develop a process to produce lower molecular weight polyesters with temporary crosslinks or branches to increase melt viscosity and strength for spinning, which does not form a solid in the presence of water.
Alkali metal salts of 5-sulfoisophthalic acids or their esters such as sodium sulfoisophthalic acid (Na-SIPA), sodium dimethylsulfoisophthalate (Na-DMSIP), and bis(2-hydroxyethyl) sodium 5-sulfoisophthalate (Na-SIPEG) have been studied to produce pilling resistant fibers. Unfortunately, to obtain desired pilling resistant properties, Na-SIPA or Na-SIPEG must be added at 3 to 10% by weight of polymer. Since Na-SIPA and Na-SIPEG cost about ten times more than TPA or DMT, the copolymer is much more expensive. In addition, this copolymer can only be hydrolyzed in acidic solution. A further problem with this copolymer is that melt viscosity is increased by the self association of the sodium sulfoisophthalate (Na-SIP) chain, not by molecular bonds. Therefore, even though the melt viscosity is high, the polymer strength is low and spinning performance is poor.
An additional consideration for producing polyester polymers is the rate of crystallization of the partially oriented polyester polymer during spinning. Normal spinning speeds for partially oriented polyester polymers are typically on the order of about 3000-3500 m/min. At higher spinning speeds, however, crystallization of the partially oriented polyester polymer occurs too fast, which results in low orientation in fibers and deteriorates physical properties such as tenacity, elongation, and shrinkage.
To increase productivity and spin at higher speeds, such as speeds of 4000-5000 m/min., additives are injected to decrease the crystallization rate of the polyester polymer. These additives include, for example, (i) a permanent crosslinker such as trimellitic acid that is added during the polymerization process or (ii) a liquid crystal polymer that is added to the polyester transfer line. Unfortunately, the permanent crosslinker and liquid crystal polymer often introduce undesirable changes to the physical properties of the polyester polymer fiber, such as higher brittleness and lower tenacity and elongation.
Accordingly, there is also a desire to decrease the crystallization rate of the polyester polymer during spinning without adversely altering the physical properties of the polyester polymer fiber.
The present invention provides a process for increasing the pill resistance of a polyester polymer, wherein the polyester polymer is produced by polymerizing a polymerization mixture comprising (a) a carbonyl compound or an oligomer of the carbonyl compound and (b) a glycol. The process comprises contacting the polymerization mixture with a cross-linker comprising (RO)mSi(X)nZp, wherein:
R is hydrogen, a hydrocarbon, or a hydrocarbon oxygen;
X is a hydrocarbon or a hydrocarbon oxygen;
Z is a hydrophilic group;
m is 1 to 3;
n is 1 to 3; and
p is 1 to 30.
The invention also provides a process for decreasing the crystallization rate of a polyester polymer during a spinning, wherein said polyester polymer is produced by polymerizing a polymerization mixture that comprises (a) a carbonyl compound or an oligomer of said carbonyl compound and (b) a glycol, said process comprising contacting said polymerization mixture with a cross-linker comprising (RO)mSi(X)nZp, wherein:
R is hydrogen, a hydrocarbon or a hydrocarbon oxygen;
X is a hydrocarbon or a hydrocarbon oxygen;
Z is a hydrophilic group;
m is 1 to 3;
n is 1 to 3; and
p is 1 to 30.
In another embodiment of the invention, the polyester polymer is produced by polymerizing a polymerization mixture that comprises a carbonyl compound or an oligomer of the carbonyl compound, wherein the carbonyl compound is HOxe2x80x94R2xe2x80x94COOH, wherein R2 is (i) hydrogen, (ii) a hydrocarbon having 1 to 30 carbon atoms, or (iii) a hydrocarbon oxygen group having 1 to 30 carbon atoms and 1 to 20 oxygen atoms.
The invention also includes a pill resistant polyester polymer produced by the aforementioned process. The process of the invention increases the melt viscosity and strength of the polyester polymer temporarily. In addition, the process of the invention decreases the crystallization rate of the polyester polymer during spinning.
In one embodiment of the invention, the cross-linker is added to the polymerization mixture before or during esterification of the carbonyl compound or oligomer. In another embodiment, the cross-linker is added to the polymerization mixture before or during transesterification of the carbonyl compound or oligomer. In yet another embodiment of the invention, the cross-linker is added to the polymerization mixture before, during, or after polycondensation of the carbonyl compound or oligomer.
The cross-linker of the invention lightly crosslinks or branches polyester molecules, and thereby increases the melt viscosity of the polyester polymer. The bonds of the branches or crosslinks are broken down after spinning the polyester polymer by hydrolysis in water, moisture, an alcohol, a weak acid, or a weak base.
In one embodiment, the cross-linker of the invention comprises (RO)mSi(X)nZp wherein:
R is hydrogen, an alkyl group containing 1 to 30 carbon atoms, a hydroxyalkyl group containing 1 to 30 carbon atoms, or a polyoxyalkyl group containing 1 to 30 carbon atoms and 1 to 20 oxygen atoms;
X is hydrogen, an alkyl group containing 1 to 30 carbon atoms, a hydroxyalkyl group containing 1 to 30 carbon atoms, or a polyoxyalkyl group containing 1 to 30 carbon atoms and 1 to 20 oxygen atoms; and
Z is a carboxylic acid or a salt thereof, sulfonic acid or a salt thereof, an amine, a nitrile, an isocyan, a hydroxy, an alkyl oxide, an epoxy alkane, an epoxy alkene, an epoxy alkyne, 1,4-dioxane, a tetrahydrofuran, or a combination of two or more thereof.
In another embodiment, the cross-linker comprises HOxe2x80x94CH2CH2xe2x80x94Si(OCH2CH2OH)3, HOxe2x80x94CH2CH(OH)CH2xe2x80x94Si(OCH3)3, or HOxe2x80x94CH2CH(OH)CH(OH)CH2xe2x80x94Si(OCH3)3. In yet another embodiment, the cross-linker comprises 3-glycidoxypropyltrimethoxysilane.
The term xe2x80x9ccross-linkerxe2x80x9d as used herein refers to a compound that lightly crosslinks or branches polyester molecules, and thereby increases the melt viscosity of the polyester polymer. The bonds of the branches or crosslinks formed by the cross-linker are then broken down after spinning by hydrolysis in water, moisture, alcohol, weak acid, or weak base. The cross-linker of the invention comprises (RO)mSi(X)nZp, wherein:
R is hydrogen, a hydrocarbon, or a hydrocarbon oxygen;
X is a hydrocarbon or a hydrocarbon oxygen;
Z is a hydrophilic group;
m is 1 to 3;
n is 1 to 3; and
p is 1 to 30.
In one embodiment of the invention, the cross-inker comprises (RO)mSi(X)nZp, wherein:
R is hydrogen, an alkyl group containing 1 to 30 carbon atoms, a hydroxyalkyl group containing 1 to 30 carbon atoms, or a polyoxyalkyl group containing 1 to 30 carbon atoms and 1 to 20 oxygen atoms;
X is hydrogen, an alkyl group containing 1 to 30 carbon atoms, a hydroxyalkyl group containing 1 to 30 carbon atoms, or a polyoxyalkyl group containing 1 to 30 carbon atoms and 1 to 20 oxygen atoms; and
Z is a carboxylic acid or a salt thereof, sulfonic acid or a salt thereof, an amine, a nitrile, an isocyan, a hydroxy, an alkyl oxide, an epoxy alkane, an epoxy alkene, an epoxy alkyne, 1,4-dioxane, a tetrahydrofuran, or a combination of two or more thereof.
In another embodiment, the cross-linker comprises HOxe2x80x94CH2CH2xe2x80x94Si(OCH2CH2OH)3, HOxe2x80x94CH2CH(OH)CH2xe2x80x94Si(OCH3)3, or HOxe2x80x94CH2CH(OH)CH(OH)CH2xe2x80x94Si(OCH3)3. In yet another embodiment, the cross-linker comprises 3-glycidoxypropyltrimethoxysilane (GTMS).
The crosslinks formed by Sixe2x80x94O bonds are temporary, because the Sixe2x80x94O bonds break down in the presence of moisture, water, an alcohol, a weak acid, or a weak base. However, the Sixe2x80x94C bond or bonds are permanent; they will not break down in the presence of moisture, water, alcohol, weak acid, or weak base. The hydrophilic group in the Sixe2x80x94C chain makes the silane compound soluble in water and glycol and, as a result, a solid does not form. For this reason, the crosslinker comprising (RO)mSi(X)nZp can be used in TPA process, where there is water byproduct, without forming a solid in recycle glycol.
Tetraethoxysilane (TEOS, Si(OCH2CH3)), however, forms sand or solid in the recycle glycol of TPA process due to water byproduct, because there are no Sixe2x80x94C bonds and all four Sixe2x80x94O bonds break in water. Silane compounds that contain Sixe2x80x94C bonding without a hydrophilic group would also form solid in recycle glycol of TPA process, such as vinyltrimethoxysilane (CH2xe2x95x90CHxe2x80x94Si(OCH3)3) or diphenylsilanediol ((C6H5)2Si(OH)2), because those silane compounds are not soluble in water and glycol.
One aspect of the invention relates to a process for increasing the pill resistance of a polyester polymer. One of the most common approaches to produce pilling resistant polyester fibers is to make a low molecular weight and low strength polyester.
Unfortunately, low molecular weight polyester is difficult to spin because the strength of the polyester is too low. Temporary cross-linker (RO)mSi(X)nZp can be added to increase the molecular weight or melt viscosity to obtain temporarily higher strength for spinning. After spinning, the temporary cross-linked bonds break down in the presence of moisture, water, an alcohol, a weak acid, or a weak base. The low molecular weight and low strength polyesters provide increased pilling resistance.
The present invention also provides a process for higher speed spinning to increase assets productivity.
The normal spinning speed for partially oriented yarn is 3000 to 3500 meter/min. Spinning speed is limited by the crystallization rate during spinning, because higher speed spinning induces a higher crystallization rate that reduces spun orientation and deteriorates the physical properties of the fiber, such as tenacity and elongation. Cross-linker (RO)mSi(X)nZp can be added to polyester to reduce the crystallization rate during spinning, therefore spinning speed can be increased such that a desired product is achieved with acceptable levels of crystallization and orientation. The increase of the spinning speed can be determined by one of skill in the art with routine experimentation. The cross-linker can be added to the polymerization mixture before or during polymerization to reduce the crystallization of the polyester polymer that results from spinning.
The cross-linker of the invention that comprises (RO)mSi(X)nZp can be dissolved in a solvent in any suitable manner and in any suitable container, vessel, or reactor at ambient temperature or elevated temperatures from 0xc2x0 C. to 220xc2x0 C. Examples of suitable solvents include, but are not limited to, water, alkyl alcohol, ethylene glycol, propylene glycol, isopropylene glycol, butylene glycol, 1-methyl propylene glycol, pentylene glycol, diethylene glycol, triethylene glycol, polyethylene glycols, polyoxyethylene glycols, polyoxypropylene glycols, polyoxybutylene glycols, and combinations of two or more thereof. A preferred glycol is an alkylene glycol, such as ethylene glycol or 1,3-propanediol, because the polyester produced using an alkylene glycol has a wide range of industrial applications.
The cross-linker can be added to the polymerization process before, during, or after transesterification or esterification of the carbonyl compound or an oligomer of the carbonyl compound. Similarly, the cross-linker can be added before, during, or after polycondensation of the carbonyl component or an oligomer of the carbonyl compound.
In one embodiment of the process of the invention, the polyester polymer is produced by polymerizing a polymerization mixture comprising (a) a carbonyl compound or an oligomer of a carbonyl compound and (b) a glycol. Any carbonyl compound which, when combined with a glycol, can produce a polyester can be used. Such carbonyl compounds include, but are not limited to, acids, esters, amides, acid anhydrides, acid halides, salts of carboxylic acid oligomers or polymers having repeat units derived from an acid, or combinations of two or more thereof. A preferred acid is an organic acid such as a carboxylic acid or salt thereof. The oligomer of a carbonyl compound such as TPA and glycol generally has a total of about 2 to about 100, preferably from about 2 to about 20 repeat units derived from the carbonyl compound and glycol.
The organic acid or ester thereof can have the formula R2COOR2 in which each R2 is independently selected from (i) hydrogen, (ii) a hydrocarboxyl radical having a carboxylic acid group at the terminus, or (iii) a hydrocarbyl radical in which each radical has 1 to 30, preferably about 3 to about 15, carbon atoms per radical which can be an alkyl, alkenyl, aryl, alkaryl, aralkyl radical, or combination of two or more thereof. The presently preferred organic acid or ester thereof has the formula R2O2CACO2R2 in which A is an alkylene group, arylene group, alkenylene group, or combination of two or more thereof and each R2 is the same as above. Each A has 2 to 30, preferably about 3 to about 25, more preferably about 4 to about 20, and most preferably 4 to 15 carbon atoms per group. Examples of suitable organic acids include, but are not limited to, terephthalic acid, isophthalic acid, napthalic acid, succinic acid, adipic acid, phthalic acid, glutaric acid, oxalic acid, maleic acid, and combinations of two or more thereof. Examples of suitable esters include, but are not limited to, dimethyl adipate, dimethyl phthalate, dimethyl terephthalate, dimethyl isophthalate, dimethyl glutarate, and combinations of two or more thereof.
The presently preferred organic diacid is terephthalic acid or its ester dimethyl terephthalate because the dyeable polyesters produced therefrom have a wide range of industrial applications.
Any suitable condition to effect the production of a polyester can include a temperature in the range of from about 150xc2x0 C. to about 500xc2x0 C., preferably about 200xc2x0 C. to about 400xc2x0 C., and most preferably 250xc2x0 C. to 300xc2x0 C. under a pressure in the range of from about 0.001 to about 1 atmosphere for a time period of from about 0.2 to about 20 hours, preferably about 0.3 to about 15 hours, and most preferably 0.5 to 10 hours.
The molar ratio of the glycol to carbonyl compound can be any ratio so long as the ratio can effect the production of an ester or polyester. Generally the ratio can be in the range of from about 1:1 to about 10:1, preferably about 1:1 to about 5:1, and most preferably 1:1 to 4:1. The polyester produced by the invention process can comprise about 1 to about 1000 parts per million by weight (ppm) of antimony and about 1 to about 200 ppm, preferably about 5 to about 100 ppm, of phosphorus.
Optionally, a catalyst can be added to the polymerization process. The catalyst can be added before or during esterification, before or during transesterification, or before or during polycondensation. The catalyst can be an antimony, aluminum, cobalt, titanium, manganese, or zinc catalyst commonly employed in the manufacture of polyester. A preferred antimony compound can be any antimony compound that is substantially soluble in a solvent disclosed above. Examples of suitable antimony compounds include, but are not limited to, antimony oxides, antimony acetate, antimony hydroxides, antimony halides, antimony sulfides, antimony carboxylates, antimony ethers, antimony glycolates, antimony nitrates, antimony sulfates, antimony phosphates, and combinations of two or more thereof. The catalyst can be present in the range of about 0.001 to about 30,000 ppm of the medium comprising the carbonyl compound and glycol, preferably about 0.1 to about 1,000 ppm, and most preferably 1 to 100 ppm by weight. A cocatalyst, if present, can be in the range of from about 0.01 to about 1,000 ppm of the reaction medium.
The invention process can also be carried out using conventional melt or solid state techniques and in the presence or absence of a toner compound to reduce the color of a polyester produced. Examples of toner compounds include, but are not limited to, cobalt aluminate, cobalt acetate, Carbazole violet (commercially available from Hoechst-Celanese, Coventry, R.I., USA, or from Sun Chemical Corp, Cincinnati, Ohio, USA), Estofil Blue S-RLS(copyright) and Solvent Blue 45(trademark) (from Sandoz Chemicals, Charlotte, N.C., U.S.A), and CuPc Blue (from Sun Chemical Corp, Cincinnati, Ohio, U.S.A). These toner compounds are well known to those skilled in the art. The toner compound can be used with the catalyst disclosed herein in the amount of about 0.1 ppm to 1000 ppm, preferably about 1 ppm to about 100 ppm, based on the weight of polyester polymer produced.
The process of the invention can also be carried out using a conventional melt or solid state technique and in the presence or absence of an optical brightening compound to reduce the yellowness of the polyester produced. Examples of optical brightening compounds include, but are not limited to, 7-naphthotriazinyl-3-phenylcoumarin (commercial name xe2x80x9cLeucopure EGMxe2x80x9d, from Sandoz Chemicals, Charlotte, N.C., USA.) and 4,4xe2x80x2-bis(2-benzoxazolyl) stilbene (commercial name xe2x80x9cEastobritexe2x80x9d, from Eastman Chemical, Kingsport, Tenn., USA). These optical brightening compounds are well known to those skilled in the art. The optical brightening compound can be used with the catalyst disclosed herein in the amount of about 0.1 ppm to 10,000 ppm, preferably about 1 ppm to about 1,000 ppm, based on the weight of polyester polymer produced.